As a child, Steve Thompson displayed outsized reactions to ordinary events and intense mood swings. By age 12, doctors diagnosed him with bipolar disorder.

The idea that he had a chronic mental illness - one typically marked in adulthood by manic periods followed by depression - frightened him. “It’s something you think you’ll have your entire life,’’ said Thompson, a 23-year-old student at Massasoit Community College in Brockton.

But over the past year, with the help of his longtime psychiatrist, he has weaned himself off mood-altering medication. The result, he said, is a new diagnosis of, at most, mild anxiety.

Patients like Thompson are at the center of a heated debate among child psychiatrists over whether a glaring 40-fold increase within a decade in bipolar diagnoses in children is genuine or the result of routine misdiagnoses.

To address this issue, a panel appointed by the American Psychiatric Association is urging that a new, potentially more transient and less-stigmatizing diagnosis - “disruptive mood dysregulation disorder’’ - be added to the official manual of mental illnesses, which is undergoing a sweeping revision.

The new condition would apply to children who have chronic irritability, as well as recurrent temper outbursts - three or more times a week, on average - that are “grossly out of proportion’’ to the situation the child confronts.

It can be as disabling to a young child as bipolar disorder, but would probably be treated with antidepressants, not antipsychotic drugs. As adults, these children would be more likely to develop anxiety or depression, rather than bipolar disorder.

‘People are just so afraid of their child being diagnosed with bipolar.’

The proposal to add the new diagnosis to the profession’s highly influential manual of mental disorders has renewed scrutiny of a psychiatric unit at Massachusetts General Hospital, which has been credited - and berated in some quarters - for its role in the nation’s more aggressive diagnosis and medication of children with bipolar disorder. Critics accuse the Mass. General unit of driving the sharp increase in bipolar diagnoses.

Proponents of the new mood disorder challenge the views of researchers at the pediatric bipolar unit at Mass. General, led largely by Drs. Joseph Biederman and Janet Wozniak, who have argued that youthful chronic irritability may be interpreted as a child’s way of manifesting a manic episode, which has been one of the central symptoms required for a bipolar diagnosis. Until Biederman and Wozniak produced their research, the disorder was largely an adult disorder and confined to those who showed distinct episodes of mania and depression.

With this new, more flexible definition of childhood bipolar disorder, rates jumped. A national study published in 2007 showed a surge in use of the bipolar diagnosis in children: the frequency of visits to doctors’ offices by youths 19 and younger for treatment of the condition increased from 25 per 100,000 visits in 1994-95 to 1,003 per 100,000 visits in 2002-03.

MATTHEW J. LEE/GLOBE STAFF

Steve (right) and David Thompson visited the PAX East gaming festival last month in Boston. Over the years, Steve has weaned himself off his mood-altering medications, to good effect.

Some top mental health specialists, while critical of this surge in diagnoses of bipolar disorder in young people, do not see the proposed new disorder as the answer. One prominent psychiatrist said both conditions are part of the profession’s tendency to rely on limited research to oversimplify, pathologize, and medicate stormy but potentially normal passages through childhood.

“It is ridiculous and reckless to include an untested diagnosis in an official diagnostic manual that will profoundly affect people’s lives,’’ said Dr. Allen Frances of Duke University School of Medicine, who was chairman of the panel in the mid-1990s that approved the latest version of the diagnostic manual.

In e-mail responses to Globe questions, Frances said that adding the new disorder would be tantamount to a “dangerous public health experiment.’’

What is ultimately added, subtracted, or revised in the Diagnostic and Statistical Manual of Mental Disorders, first put out by the American Psychiatric Association in 1952, is loaded with practical and cultural implications.

It will help define what is considered normal behavior. It largely determines how clinicians diagnose conditions; what health insurers will pay for; what drugs are made and marketed; and what research will be funded by governments and foundations. Panels of specialists within the professional organization are debating all categories of diagnoses in the manual, and the psychiatric association is expected to make final decisions in time for its fifth revised edition to be published in May 2013.

The leading researcher behind the new disruptive-mood diagnosis is Dr. Ellen Leibenluft of the National Institute of Mental Health. She is also one of eight members of the childhood disorders panel of the American Psychiatric Association, which is pushing for the addition of the disorder. The chairman of the panel is Dr. Daniel Pine, a colleague of Leibenluft at the institute who has coauthored papers with her on this new disorder.

Leibenluft and Pine declined Globe request for interviews.

When asked about panel members’ involvement in research on the disorder, a spokeswoman for the psychiatric association released a statement saying the organization is confident it can objectively scrutinize all proposals.

Leibenluft’s work on the disorder can be gleaned from her research papers, as well as by a memo put out by her, Pines, and others on the psychiatric association’s childhood panel. They argue that there is a subset of children diagnosed with bipolar disorder whose symptoms, largely chronic irritability, better fit the new diagnosis and should be treated differently. The panel says this diagnosis should not be made before the age of 6, and onset is generally before age 10.

But, in a telephone interview with the Globe, Wozniak of Mass. General maintained that chronic irritability in children is a potential marker of bipolar disorder, though only if it takes on an aggressive form over sustained periods, which includes not just rudeness or whining, but spitting, hitting, and threats of destruction.

She said she does not think a child must remain diagnosed with bipolar disorder through adulthood for the original diagnosis to be considered accurate. Some children diagnosed with the disorder appear to get better over time, often for unexplained reasons, she said. She said one study found that 44 percent of children diagnosed with bipolar disorder continued to have the condition in adulthood.

Wozniak, who opposes the new mood-disorder diagnosis, said she fears that its focus on temper and irritability may capture too many normal but volatile children or delay what might be an appropriate bipolar diagnosis and treatment. Accepting the proposed disorder, she said, is “misguided and unconscionable.’’

Some other local clinicians applauded Leibenluft for challenging what they describe as excessively flexible criteria used to diagnose bipolar disorder in children, leading to an explosion in new cases. They said clinicians should consider other complex causes for severe mood problems, including family trauma or developmental delays.

“She and her group have done a tremendous service to the field,’’ said Dr. Jennifer Harris, a child psychiatrist and clinical supervisor at Cambridge Hospital.

Steve Thompson’s mother worries that doctors and others are fixated on diagnostic names and eliminating the stigmatizing sound of “bipolar,’’ rather than focusing on how to better evaluate and treat children with debilitating mood disorders. Susan Page-Thompson and her son wonder whether he had the new disorder, but she is pleased her son has shown profound improvement and said he received good treatment in the past.

“People are just so afraid of their child being diagnosed with bipolar,’’ she said.